1. Field of the Invention
This invention relates to a modulator for modulating a carrier wave with an in-phase component (I component) signal and a quadrature component (Q component) and a demodulator for demodulating the in-phase component signal and quadrature component signal, particularly to a technology enabling broadband modulation and demodulation with simple control.
2. Description of the Prior Art
In, for example, intelligent transport systems (ITS) used to increase traffic efficiency through exchange of information among people, vehicles and roads, consideration is being given to use of software radio that uses software to send and receive wireless signals.
Wireless devices such as software radios need to be equipped with modulator and demodulator units for high-frequency and/or broadband wireless communication.
An example configuration of a modulator-demodulator unit conventionally used for analog modulation-demodulation will be explained.
FIG. 5 shows the configuration of an analog quadrature modulator provided downstream of a digital unit D21. Although the digital unit D21 is included in the drawing for convenience of explanation, it should be noted that the digital unit D21 would not ordinarily be a component of an analog quadrature modulator.
In the analog quadrature modulator shown in the figure, an in-phase component signal output by the digital unit D21 is input to an in-phase component side mixer (MIX) MI21 and a quadrature component signal output by the digital unit D21 is input to a quadrature component side mixer (MIX) MQ21.
Further, in this analog quadrature modulator, a local signal generator (OSC) OSC11 generates a signal having the frequency of, for instance, a carrier wave signal ordinarily used in communication (carrier wave frequency) and the signal having this carrier wave frequency is output as an in-phase component carrier wave signal to the in-phase component side mixer MI21 without modification and the signal having the carrier wave frequency is also output to a 90-degree (xc2x0) phase shifter P11. The 90-degree phase shifter P11 shifts the signal received from the local signal generator OSC11 90 degrees and outputs the phase-shifted signal to the quadrature component side mixer MQ21 as a quadrature component carrier wave signal.
The in-phase component side mixer MI21 mixes the in-phase component carrier wave signal received from the local signal generator OSC11 and the in-phase component signal received from the digital unit D21 to modulate the in-phase component carrier wave signal with the in-phase component signal and outputs the resulting in-phase modulated component.
The quadrature component side mixer MQ21 mixes the quadrature component carrier wave signal received from the 90-degree phase shifter P11 and the quadrature component signal received from the digital unit D21 to modulate the quadrature component carrier wave signal with the quadrature component signal and outputs the resulting quadrature modulated component.
In this analog quadrature modulator, the in-phase modulated component output by the in-phase component side mixer MI21 and the quadrature modulated component output by the quadrature component side mixer MQ21 are synthesized and synthesized signal is output as a composite signal. The composite signal is a carrier wave frequency signal including, for example, amplitude information and phase information. By controlling the in-phase component signal and the quadrature component signal output by the digital unit D21 to modify the amplitude information and the phase information, data to be transmitted by frequency modulation, phase modulation and/or amplitude modulation can be transmitted on the carrier wave. In addition, the composite signal output by the analog quadrature modulator can be wirelessly transmitted to another party""s wireless device as a wireless signal via an antenna or the like (not shown).
The configuration of an analog quadrature demodulator will now be explained with reference to FIG. 6.
The analog quadrature demodulator illustrated in the drawing is input with a carrier wave frequency composite signal including amplitude information or phase information, specifically with a signal transmitted wirelessly from, for example, a wireless device with which communication is to be conducted and received wirelessly via an antenna (not shown). The received composite signal is divided and input to an in-phase component side mixer MI22 and a quadrature component side mixer MQ22.
Similarly to the case of the analog quadrature modulator shown in FIG. 5, in this analog quadrature demodulator, a local signal generator (OSC) OSC12 generates a signal of, for instance, a carrier wave frequency and the signal having this carrier wave frequency is output as an in-phase component carrier wave signal to the in-phase component side mixer MI22 without modification and the signal having the carrier wave frequency is also output to a 90-degree phase shifter P12, which shifts it 90 degrees and outputs the phase-shifted signal to the quadrature component side mixer MQ22 as a quadrature component carrier wave signal.
The in-phase component side mixer MI22 mixes the in-phase component carrier wave signal received from the local signal generator OSC12 and the composite signal to demodulate the in-phase modulated component contained in the composite signal with the in-phase component carrier wave signal and outputs the in-phase component signal produced by the demodulation.
The quadrature component side mixer MQ22 mixes the quadrature component carrier wave signal received from the 90-degree phase shifter P12 and the composite signal to demodulate the quadrature modulated component contained in composite signal with the quadrature component carrier wave signal and outputs the quadrature component signal produced by the demodulation.
The in-phase component signal and the quadrature component signal output by the analog quadrature demodulator are, for example, output to a downstream digital unit (not shown) to acquire receive data based on to the in-phase component signal and the quadrature component signal.
There will now be explained a configuration for changing the carrier wave frequency used in modulation and demodulation in the analog quadrature modulator shown in FIG. 5 and the analog quadrature demodulator shown in FIG. 6.
Carrier wave frequency change is required, for example, in a wireless device or the like that sends and receives wireless signals by switching among and using carriers of different frequencies spread over a broad band.
In the analog quadrature modulator shown in FIG. 5 and the analog quadrature demodulator shown in FIG. 6, a configuration enabling carrier wave frequency change can conceivably be implemented, for instance, by installing voltage-controlled oscillators (VCOs) in place of the local signal generators OSC11 and OSC12 and controlling the voltage applied to the voltage-controlled oscillators to change the frequency of the signals (local signals) output from the voltage-controlled oscillator to the in-phase component side mixers MI21, MI22 and the 90-degree phase shifters P11, P12. With this configuration, however, the fact that the devices constituting the 90-degree phase shifters P11, P12 have frequency characteristics would make it possible to achieve accurate 90-degree phase shift only in a relatively narrow band, i.e., frequencies would be present in the required broad band at which a phase shift greater than 90 degrees or less than 90 degrees arose, making modulation-demodulation impossible over a broad band.
While it is conceivable to overcome this problem by providing multiple 90-degree phase shifters associated with different frequencies and using a switch or the like to switch to the one to be used at each frequency, this configuration would complicate the control, raise cost and increase circuit size, because it would require provision of phase shifters for the individual frequencies and also increase the number of control system signals.
In the modulator taught by JP-A-HEI-5-207080, for example, a synthesizer generates a frequency signal for each channel and, at the time of shifting the phase of the synthesizer output 90 degrees using a variable 90-degree phase shifter, the variable 90-degree phase shifter is controlled to make the error of a detected quadrature phase zero. However, this configuration requires a circuit for detecting quadrature phase and a circuit for controlling the 90-degree phase shifter to make the quadrature phase error zero. Control therefore becomes complicated and, moreover, it is difficult to achieve high accuracy with the variable phase shifter in a high-frequency band such as the quasi-microwave band.
In the quadrature phase signal generator circuit taught by JP-A-HEI-10-243037, for example, in order to cause a voltage-controlled oscillator (VCO) to generate a signal whose phase is 90 degrees different from that of a signal output by a local oscillator (local signal), the voltage-controlled oscillator is controlled based on a comparison of the frequency difference and phase difference of the two signals. With this configuration, however, when multiple channels are used, for example, the frequency of the signal output by the voltage-controlled oscillator must be controlled every time the frequency of the local signal is switched, and phase control of the signal is also necessary. The control therefore becomes complicated.
As explained with regard to the prior art, in a conventional modulator like that shown in FIG. 5 or demodulator like that shown in FIG. 6, modulation or demodulation over a broad band entails complex control, requires large circuitry and increases cost.
The present invention was accomplished in light of such problems of the prior art and has as its object to provide a modulator that when modulating a carrier wave with an in-phase component signal and a quadrature component signal can achieve broadband modulation with simple control.
Another object of the present invention is to provide a demodulator that when demodulating a carrier wave frequency composite signal into an in-phase component signal and a quadrature component signal can achieve broadband demodulation with simple control.
The modulator and demodulator according to the present invention enable reduction of circuit size and cost in comparison with the prior art.
In order to achieve the foregoing object, the modulator according to the invention modulates a carrier wave signal for a carrier wave signal with an in-phase component signal and modulates a carrier wave signal for a quadrature component with a quadrature component signal, in the following manner.
Specifically, a fixed frequency signal generating means generates two signals of fixed frequency differing 90 degrees in phase, a variable frequency signal generating means generates a signal whose frequency can be varied according to a modulated signal to be produced, an in-phase component carrier wave signal generating means mixes one signal generated by the fixed frequency signal generating means and the signal generated by the variable frequency signal generating means to generate a carrier wave signal for an in-phase component, a quadrature component carrier wave signal generating means mixes the other signal generated by the fixed frequency signal generating means and the signal generated by the variable frequency signal generating means to generate a carrier wave signal for a quadrature component, an in-phase component modulating means modulates the in-phase component carrier wave signal generated by the in-phase component carrier wave signal generating means with the in-phase component signal and a quadrature component modulating means modulates the quadrature component carrier wave signal generated by the quadrature component carrier wave signal generating means with the quadrature component signal.
Therefore, since two fixed-frequency signals that differ 90 degrees in phase are generated, it is easy to ensure that the phase difference between the two signals is exactly 90 degrees. In addition, since the frequency of the signal generated by the variable frequency signal generating means according to the frequency of the modulated signal to be produced can be controlled and changed so as to change the frequency of the carrier wave signals for the in-phase component and the quadrature component, broadband modulation can be achieved with simple control.
The fixed frequency signal generating means can, for example, be constituted using a digital unit or be constituted using a local signal oscillator and a 90-degree phase shifter.
In one configuration of the modulator according to the present invention, the fixed frequency signal generating means is constituted using a local signal oscillator that generates a fixed frequency and a 90-degree phase shifter that shifts the phase of the signal generated by the local signal oscillator 90 degrees. In this case, one or the other of the signal generated by the local signal oscillator and the signal phase-shifted by the 90-degree phase shifter is mixed by the in-phase component carrier wave signal generating means and the remaining signal is mixed by the quadrature component carrier wave signal generating means.
As the carrier wave signal for the in-phase component or the quadrature component there is, for example, used a signal having the frequency of a carrier wave ordinarily used in communication and when multiple carrier wave frequencies are used, the multiple carrier wave frequency signals are switched according to, for example, the communication conditions.
The fixed frequency is not particularly limited and can be set at any of various values based on the use conditions of the modulator.
The control for changing the frequency of the signal generated by the variable frequency signal generating means according to the frequency of the modulated signal to be produced is ordinarily conducted in a mode of matching with the frequency of the carrier wave used for communication, i.e. for transmission of the frequency of the generated in-phase component carrier wave signal or the frequency of the generated quadrature component carrier wave signal.
The signal generated by the variable frequency signal generating means is divided into two signals having the same phase, one divided signal is mixed by the in-phase component carrier wave signal generating means, and the other divided signal is mixed by the quadrature component carrier wave signal generating means.
When the in-phase component carrier wave signal generating means or the quadrature component carrier wave signal generating means generates the in-phase component carrier wave signal or the quadrature component carrier wave signal, unnecessary frequency components are preferably removed from the mixing result of the means by a filter.
The in-phase component modulating means and the quadrature component modulating means are, for example, constituted as mixers. For example, the in-phase component carrier wave signal and the in-phase component signal are mixed to produce an in-phase modulated component, and the quadrature component carrier wave signal and the quadrature component signal are mixed to produce a quadrature modulated component. The in-phase modulated component and the quadrature modulated component are, for example, synthesized to obtain a composite signal including amplitude information or phase information.
Further, the demodulator according to the invention demodulates an in-phase component modulated signal with an in-phase component carrier wave signal to produce an in-phase component signal, and demodulates a quadrature component modulated signal with a quadrature component carrier wave signal to produce a quadrature component signal, in the following manner.
Specifically, a fixed frequency signal generating means generates two signals of fixed frequency differing 90 degrees in phase, a variable frequency signal generating means generates a signal whose frequency can be varied according to a modulated signal, an in-phase component carrier wave signal generating means mixes one signal generated by the fixed frequency signal generating means and the signal generated by the variable frequency signal generating means to generate a carrier wave signal for an in-phase component, a quadrature component carrier wave signal generating means mixes the other signal generated by the fixed frequency signal generating means and the signal generated by the variable frequency signal generating means to generate a carrier wave signal for a quadrature component, an in-phase component demodulating means demodulates an in-phase component modulated signal with the in-phase component carrier wave signal generated by the in-phase component carrier wave signal generating means to produce an in-phase component signal, and a quadrature component demodulating means demodulates a quadrature component modulated signal with the quadrature component carrier wave signal generated by the quadrature component carrier wave signal generating means to produce a quadrature component signal.
Therefore, since two fixed-frequency signals that differ 90 degrees in phase are generated, it is easy to ensure that the phase difference between the two signals is exactly 90 degrees. In addition, since the frequency of the signal generated by the variable frequency signal generating means according to the frequency of the modulated signal to be demodulated can be controlled and changed so as to change the frequency of the carrier wave signals for the in-phase component and the quadrature component, broadband demodulation can be achieved with simple control.
The fixed frequency signal generating means can, for example, be constituted using a digital unit or be constituted using a local signal oscillator and a 90-degree phase shifter.
In one configuration of the demodulator according to the present invention, the fixed frequency signal generating means is constituted using a local signal oscillator that generates a fixed frequency and a 90-degree phase shifter that shifts the phase of the signal generated by the local signal oscillator 90 degrees. In this case, one or the other of the signals generated by the local signal oscillator and the signal phase-shifted by the 90-degree phase shifter is mixed by the in-phase component carrier wave signal generating means and the remaining signal is mixed by the quadrature component carrier wave signal generating means.
Although the general practice is for the in-phase component modulated signal or the quadrature component modulated signal to be processed for demodulation in the form of, for example, a composite signal synthesizing the two component modulated signals, the two component modulated signals can instead be processed in the form of separate signals. In this case, too, the component signal of each component modulated signal can be demodulated with the corresponding component carrier wave signal.
As the carrier wave signal for the in-phase component or the quadrature component there is, for example, used a signal having the same frequency as the in-phase component or quadrature component modulated signal to be demodulated and when modulated signals of multiple frequencies are demodulated, the carrier wave signals of these multiple frequencies are switched according to, for example, the communication conditions.
The fixed frequency is not particularly limited and can be set at any of various values based on the use conditions of the demodulator.
The control for changing the frequency of the signal generated by the variable frequency signal generating means according to the frequency of the demodulated is ordinarily conducted in a mode of matching the frequency of the generated in-phase component carrier wave signal or the frequency of the generated quadrature component carrier wave signal with the frequency of the modulated signal to be demodulated.
The signal generated by the variable frequency signal generating means is divided into two signals having the same phase, one divided signal is mixed by the in-phase component carrier wave signal generating means, and the other divided signal is mixed by the quadrature component carrier wave signal generating means.
When the in-phase component carrier wave signal generating means or the quadrature component carrier wave signal generating means generates the in-phase component carrier wave signal or the quadrature component carrier wave signal, unnecessary frequency components are preferably removed from the mixing result of the means by a filter.
The in-phase component modulating means and the quadrature component modulating means are, for example, constituted as mixers. For example, the in-phase component carrier wave signal and the in-phase component modulated signal are mixed to produce an in-phase component signal as an in-phase component demodulation result and the quadrature component carrier wave signal and the quadrature component modulated signal are mixed to produce a quadrature component signal as a quadrature component demodulation result, and receive data are acquired from the in-phase component signal and the quadrature component signal.